1. Field of Invention
This invention deals with the field of devices called turret winders which are used to wind webs of film type materials on cores.
A typical turret winder is comprised of a rotatable turret containing two pairs of rotating chucks located 180 degrees apart from each other at the ends of a pair of turret arms. These turret winders can produce bundles of film up to 24 to 30 inches in diameter. Turret winders with three or four pairs of chucks are also available but these winders produce smaller bundles 12 to 14 inches in diameter.
The use of two pairs of chucks to hold two cores permits the web winding to be done essentially continuously. Winding begins on one core and then after a bundle is accumulated on the core, the turret arms are rotated 180 degrees and the web is transferred to the second core and winding continues uninterrupted. Often the cores are surfaced with an adhesive strip to facilitate web transfer to the new core.
While the second core is accumulating a bundle, the first core with its bundle is removed, either manually or automatically, and a new core is loaded into the chucks. When the second core has accumulated a bundle, the turret is again rotated and the web transferred to the core in the first set of chucks. These operations are then repeated until the desired number of bundles have been wound.
When a web of film is wound, it forms a bundle of predetermined diameter corresponding to a particular length of the film material depending on the thickness of the film.
During a typical winding operation, the web is wound on a core approximately 3 5/8 inches in diameter at the rate of up to 1500 feet per minute. At the end of the winding cycle typically bundles contain 2000 to 6000 feet of film and range from 8 to 12 inches in diameter. These bundles of film are usually accumulated in two to four minutes of winding. However larger bundles containing as much as 40,000 feet of film are also wound in cycles of thirty minutes or more.
In a typical operation, the web is a deformable elastic material which must be wrapped on the bundle without entrapment of air between the accumulating layers.
A lay-on roll is usually used to eliminate the entrapment of air when the web is wound on the bundle. This lay-on roll rides on the surface of the bundle as the web is wrapped and presses the web on to the rotating bundle to prevent air from being trapped under the web as it is wrapped on the bundle. This lay-on roll also influences the tension in the web and the hardness of the bundle. The hardness is in part a function of the pressure exerted on the bundle by the lay-on roll and the counter-acting force from web tension. The resulting pressure at the nip where the lay-on roll actually presses the web onto the bundle and the tension in the web as it is wound determine bundle hardness. The web tension is adjusted by conventional means in the web feed-in system.
Proper web tension and lay-on roll pressure must be maintained to form a hard bundle without so much tension that the bundle telescopes or more typically, with film that tends to cling, a non-cylindrical barrel shaped bundle is formed. When telescoping occurs, the inner layers of a bundle are squeezed out axially resulting in a bundle width that is larger than the width of the web as it is wound. A barrel shaped bundle is narrower than the width of the unwound web and very often has circumferential wrinkles in the bundle of film. In addition, if web tension and lay-on roll pressure are to low a soft bundle is produced with wrinkles from trapped air. If web tension and lay-on roll pressure vary over too wide a range during winding this will produce a bundle with soft portions overlaid by hard portions. When this occurs a bundle with ridges induced in the soft portions by the compression from the high tension hard portions is produced. All of these irregularities can result in customer rejection of the bundle.
As indicated above, when the desired bundle diameter has been reached, the turret arms are rotated 180 degrees so that the second pair of chucks, which also hold an empty core are moved into position to begin the winding operation. In a typical application, winding of the web continues during the turret rotation operation.
This turret rotation operation typically consumes 20 to 30 seconds and approximately 300 to 500 feet of web is wound on the bundle during this operation at web winding rates of 1000 to 1500 feet per minute.
During turret rotation on a typical turret winder, lay-on roll contact with the bundle is lost. For many types of materials, when this occurs, the web that is accumulated on the bundle during the turret rotation operation traps air between the successive layers. In addition, web tension often varies substantially. These factors cause unacceptable wrapping of the web during turret rotation. This poorly wrapped portion of the web must be removed manually from the bundle and discarded or reprocessed as scrap.
At typical bundle sizes and web winding rates, this scrap can represent 10 to 15 per cent of the total web actually wound on a core.
The conventional web feed in mechanisms which function to prepare the web for winding are also the source of variations in web tension which contribute to unsatisfactory wound bundles of film.
In a typical feed in mechanism the web travels over feed rolls which are driven by a variable speed motor and a bowed roll. The bowed roll is a roll, with a rubber cylindrical sleeve mounted on a number of bearings which are supported on a cylindrical shaft which is curved or "bowed" along its longitudinal axis. As the web passes over this bowed roll the film is stretched slightly in the direction transverse to its direction of travel and any wrinkles in the web are removed.
In a conventional feed in mechanism web tension is controlled by measuring web tension, by measuring or sensing the force exerted by the web on a float roll and using that force to adjust the speed of the core chuck drive motor. The speed of the motor which controls the feed rolls must also be adjusted simultaneously to match the speed change in the core chuck drive motor. In practice, while these systems function reasonably effectively, speed variation between the chuck core drive motor and the feed roll motor cause web tension variations which adversely affect the winding operation. In addition, because the web is stretched slightly as it traverses the bowed roll and the bowed roll rotation is imparted by the web a further undesirable
2. Prior Art
There are several approaches described in the prior art relating to turret winders which incorporate lay-on rolls to control roll hardware, web tension and eliminate air entrapment.
The use of pivotally mounted pressure rolls for this purpose is known in the art. The ENGL U.S. Pat. No. 4,343,440 incorporates a pivotally mounted pressure roll as does the PENROD U.S. Pat. No. 3,478,975.
Also included among these is an apparatus and method described in the U.S. Patent of TETRO No. 4,431,140 incorporating pivotally mounted pressure rolls with accompanying guide rolls mounted on pivot arms which are mounted on plates concentric with the turret shaft axis. This device also is configured to require loading of cores on one side of the device and unloading completed bundles on the opposite side. This loading arrangement is contrary to the usual practice of loading and unloading at the same location. In addition, with the apparatus described in TETRO, when the turret is rotated from the winding position to the unloading position, the wrap angle of the web on the pressure lay-on roll is increased substantially from the angle occurring during the winding operation. Finally, the TETRO apparatus requires that an adhesive strip must be placed on a new core to facilitate the transfer of the film web to the core at the beginning of the winding process.